#2876 webp terminal: subsequent multiplot fails after unset multiplot

[Hiroki Motoyoshi]

In the webp terminal, executing a second multiplot block within the same session fails to render plot data, generating a file that contains only the WebP/RIFF header.

Interestingly, if a single plot (non-multiplot) is executed afterwards, it renders correctly, showing that normal plot operations can recover the terminal state.

set terminal webp noanimate

# 1. First multiplot -> SUCCESS
set output 'test1.webp'
set multiplot
plot x
unset multiplot
set output

# 2. Second multiplot -> FAILS (empty image / header only)
set output 'test2.webp'
set multiplot
plot x**2
unset multiplot
set output

# 3. Subsequent standard plot -> SUCCESS
set output 'test3.webp'
plot x**3
set output

• test1.webp: Valid image.
• test2.webp: Corrupted/empty (header only).
• test3.webp: Valid image.

My environment is gnuplot 6.0.4 on MacOS.